Its your wish , it would hardly make the difference I have CS4, CS5 and CS5.5 installed my machine and it works fine. However Adobe always recommend to uninstall the older veriosn before installing the newer veriosn.

Its on your usage and comfort level....You want to stick to CS4 and have CS5 along with it or you can left the old one behind and use new one,

It depends on how you use your Creative Suite. If you have sufficient disk space and/or need to be fully compatible with earlier versions, i.e. InDesign documents in Creative Suite 4, then I would recommend leaving it on your computer.

Thank you! Actually I read that an upgrade was supposed to check for the previous version and I just thought it would upgrade that version not install the new version as well. I'll leave CS4 on my machine.

Cool,, when you install the upgrade then one of teh process is to check for teh earlier version , if incase it doesnt find it installed on teh computer then it ask for the previous serial number , when entered the installation goes thorugh fine.

That the upgarde procedure ....hence I said you can keep it or remove it, all you need the CS4 serail numebr to install the software.